Processes of chemical nickel plating and baths therefor



2,847,327 Pare-med Aug. 12, less PROCESSES 9F CI EMICAL NICKEL PLATING AND BATES THEREFOR Paul Talmey, Barrington, EL, and Gregoire Gntzeit, Highland, Ind., assignors to General American TransportatYmnkCorporation, Chicago, Ill., a corporation of New No Drawing. Application {)ctober 25, 1954 Serial No. 464,592

11 Claims. (Cl. 117-130) ploying an aqueous bath of the nickel cation-hypophos phite anion type is based upon the catalytic reduction of nickel cations to metallic nickel and the corresponding oxidation of hypophosphite anions to phosphite anions with the evolution of hydrogen gas at the catalytic surface. The reactions take place when the body of catalytic material is immersed in the plating bath, and the exterior surface of the body of catalytic material is coated With nickel. The following elements are catalytic for the oxidation of hypophosphite and thus may be directly nickel-plated: iron, cobalt, nickel, ruthenium, rhodium,, palladium, osmium, iridium and platinum. The following elements are examples of materials which may be nickel-plated by virtue of the initial displacement deposition of nickel thereon either directly or through a galvanic effect: copper, silver, gold, beryllium, germanium, aluminum carbon, vanadium, molybdenum, tungsten, chromium, selenium, titanium and uranium. The following ele ments are examples of non-catalytic materials which ordinarily may not be nickel-plated: bismuth, cadmium, tin, lead and zinc. The activity of the catalytic materials varies considerably; and the following elements are particularly good catalysts in the chemical nickel plating bath; iron, cobalt, nickel and palladium. The chemical nickel plating process is autocatalytic since both the original surface of the body being plated and the nickel metal that is deposited on the surface thereof are both catalytic; and the reduction of the nickel cations to metallic nickel in the plating bath proceeds until all of the nickel cations have been reduced to metallic nickel, in the presence of an excess of hypophosphite anions, or until all of the hypophosphite anions have been oxidized to phosphite anions, in the presence of an excess of nickel cations. Actually the reactions are slowed-down rather rapidly as time proceeds because the anions, as contrasted with the cations, of the nickel salt that is dissolved in the plating bath combine with the hydrogen cations to form an acid, which, in turn, lowers the pH of the bath, and the reducing power of the hypophosphite anions is decreased as the pH value of the bath decreases. Moreover, there is a tendency for the early formation in the plating bath of a black precipitate that comprises a random chemical reduction of the nickel cations. Of course, this formation of the black precipitate comprises a decomposition of the plating bath; and is particularly objectionable in that it causes the nickel deposit to be coarse, rough and frequently porous.

For the dual purposes of increasing the stability of the plating bath (preventing the formation of the black precipitate mentioned), and of increasing the normal plating rate of the bath, various baths of the present type have been suggested employing different additives or' agents that serve either as buffers or as exaltants. For example, in U. S. Patent No. 2,658,841, granted on November 10, 1953, to Gregoire Gutzeit and Abraham Krieg, there is disclosed a chemical nickel plating bath of the nickel cation-hypophosphite anion type that contains as an additive a buffer in the form of a soluble salt of an organic acid, and specifically sodium acetate; and in U. S. Patent No. 2,658,842, granted on November 10, 1953, to Gregoire Gutzeit and Ernest J. Ramirez, there is disclosed a chemical nickel plating bath of the nickel cation-hypophosphite anion type that contains as an additive an exaltant in the form of a soluble salt of a simple short-chain saturated aliphatic dicarboxylic acid, and specifically sodium succinate. A typical chemical nickel plating bath of the character of that disclosed in the Gutzeit and Krieg patent essentially comprises an aqueous acid solution of a nickel salt and a hypophosphite and a buffer in the form of an alkaline acetate, the initial pH of the bath being within the approximate range 4.5 to 5.6, the ratio between nickel ions and hypophosphite ions in the bath being between 0.25 and 0.60, the absolute concentrations of hypophosphite ions in the bath being between 0.15 and 0.35 mole/liter, and the absolute concentrations of acetate ions in the bath being approxi mately 0.120 mole/liter. A typical chemical nickel plating bath of the character of that disclosed in the Gutzeit and Ramirez patent essentially comprises an aqueous acid solution of a nickel salt and a hypophosphite and an exaltant in the form of a salt of succinic acid, the initial pH of the bath being within the approximate range 4.3 to 6.8, the ratio between nickel ions and hypophosphite ions in the bath being between 0.25 and 1.60, the

absolute concentration of hypophosphite ions in the bath 2,658,839, granted on November 10, 1953, to Paul Talmey and William J. Crehan; which system involves periodic or continuous regeneration of the plating bath by the addition thereto of'appropriate ingredients for the purpose of maintaining substantially constant the composition of the bath.

In carrying out the chemical nickel plating process, particularly in a continuous system of the character mentioned, it has been discovered that an initially stable plating bath becomes unstable after some use, and notwithstanding the content of the bufier, or the exaltant, or both; whereby the plating bath decomposes with the formation of the previously-mentioned black precipitate. It is believed that the formation of the black precipitate (the first visible manifestation in the plating bath of random reduction of the nickel cations) starts at the surfaces of suspensoids (solid particles of dust, microcrystalline precipitate of ferric hypophosphite, nickel phosphite, etc.) present in the plating bath; and the presence of these suspensoids in the plating bath is evidenced by the observation of Tyndall beams when a shaft of light is passed through the clear filtered plating bath, even when freshly prepared.

The present invention is predicated upon the discovery that plating baths of the nickel cation-hypophosphite anion types mentioned may be stabilized to a high degree, without material depression of the plating rates thereof, by the further addition thereto of a trace amount of certain water-soluble additives of dipolar molecular character; the dipolar molecules being water-soluble in the true sense that a molecular solution is produced, as distinguished from a colloidal solution. In the bath, the cation of the dipolar molecule is readily dissociated and the anion of the dipolar molecule forms with the metallic elementof the suspensoid a Water-insoluble product that is hydrophobic or Water-repellent; the terms watererepellent and hydrophobic being taken in the broadest sense, indicating an induced surface condition that will repel anions and dipoles of negative character. Thus the additive of dipolar molecular form is of the hydrophobic film-forming class and may take a variety of forms, since these compounds have at least one [functional group With affinity for metals and a hydrophobic radical characterized by forming oriented water-repellent coatings on metal surfaces.

It is believed that the anions of the dipole molecules selectively attach themselves to the suspensoids in the plating bath forming a hydrophobic film on the surface thereof, thereby preventing the suspensoids from serving as nuclei for the random decomposition of the plating bath and the formation of the objectionable black precipitate. Specifically, the anions seem to be absorbed in an oriented manner upon the surfaces of the suspensoids giving them a hydrophobic (water-repellent) character, which may account for the protective action in inhibiting the formation of the black precipitate. It is not necessary to have a continuous film upon the surfaces of the suspensoids, as it is suflicient that the active centers be shielded. This mechanism is considered to be the most likely, as it is well-known that ions or dipoles are absorbed on the surfaces of solids due to localized attractive forces (free valency links), and that these same ions or dipoles repel each other due to their identical electric charges. Thus the packing of these ions or dipoles on a section of surface is a function of the radius of curvature of the surface, so that the smaller the radius of curvature the stronger the bond and the closer the packing. Accordingly, since the radii of the suspensoids are very small, the surfaces thereof will be preferentially and more densely covered than the relatively flat surfaces of any large body to be plated. Consequently the anions selectively attach themselves first to the suspensoids, thereby preventing their objectionable effect as nuclei for the random decomposition of the plating bath as explained above. Moreover, the amount of the additive present should be limited so as not to have an inhibiting eifect on the surface of the object being plated.

In accordance with the invention only a trace amount of the additive is placed in the bath; and specifically it has been discovered that plating baths of the character mentioned are stabilized by the presence therein of an extremely small amount of hydrophobic film-forming longchain aliphatic organic compound in which the aliphatic radical contains at least6 carbon atoms, and preferably between ,8: and 18' carbon atoms. Specifically the organic compound is selected from the class consisting offatty acids and water-soluble salts thereof, amino compounds, and sulfates and sulfonates of fatty acids and fatty alcohols. In large quantities the aliphatic radical present in the bath is a catalytic poison, and will considerably reduce theplating rate or stop plating altogether. However, at the proper level, the aliphatic radical prevents random decomposition of the plating bath and the formation of the black precipitate mentioned; the proper quantity of aliphatic radical in the plating bath to achieve stability being in the approximate range to 100 parts per 1,000,000 parts of the plating bath by weight.

In view of the foregoing, it is the primary object of. the present invention to provide an improvednickel plating process of the character described in which the reactions involved are carried out more efliciently and'under more stable conditions than heretofore, thereby rendering the process more desirable from a commercial standpoint.

Another object of the invention is to provide an improved nickel plating process of the character described, that employs a plating bath of the nickel cation-hypophosphite anion type containing as a stabilizing agent an additive of dipolar molecular character.

A further object of the invention is to provide an improved nickel plating process of the character described that comprises a plating bath of the nickel cation-hypophosphite anion type containing as a stabilizing agent a hydrophobic film-forming long-chain aliphatic organic compound in which the aliphatic radical contains at least 6 carbon atoms.

A further object of the invention is to provide an improved nickel plating process of the character described, that employs a plating bath of the type mentioned containing a stabilizing agent that increases the normal plating rate thereof.

A still further object of the invention is to provide an improved nickel plating bath of the nickel cation-hypophosphite anion type containing as a stabilizing agent a hydrophobic film-forming long-chain aliphatic organiccompound in which the aliphatic radical contains 8 to 18 carbon atoms.

These and other objects and advantages of I the invention pertain to the particular arrangement of the steps of the method and of the composition of the plating bath,

and Will be understood from the foregoing and following description. 1

In accordance with the process of the present inve tion, the article to be nickel-plated and normally formed of a catalytic material, is properly prepared by mechanically cleaning, degreasing and light pickling, substantially in accordance With standard practices in electroplating processes.

hydrochloric acid. The article is then immersed in a suitable volume of the bath containing the proper proportions of nickel cations, hypophosphite anions, buffer or exaltant, and stabilizing agent, the pH of the bath having been, if necessary, adjusted to an optimum value by the addition of an appropriate acid or base, and the bath having been heated to a temperature just below its boiling Almost immediately hydrogen bubbles are formed on the cata-- point, such as 99 C., at atmospheric pressure.

lytic surface of the steel object and escape in a steady stream from the bath, while the surface of the steel -object is slowly coated with metallic nickel (containing some phosphorus). The reaction is continued until the color of the bath (green at the start) shows the absence of nickel, or until the evolution of hydrogen stops, or

until it is determined that the required thickness of the nickel coating has been deposited on the steel object. Of

course, the steel object is then removed from the bath and' tially comprises an aqueous solution containing nickel.

cations, hypophosphite anions, a buifer or exaltant, and a stabilizing agent. Forexarnple,-the nickel cations may be derived from nickel chloride; and the hypophosphite anions may be derived from sodium, potassium, lithium,

calcium, magnesium, strontium, barium, etc., hypophosphites, or various combinations thereof. Specifically, a

suitable bath may be formed in an exceedingly simple,

manner by dissolving in a hydrochloric acid-Water ,solu-,

tion nickel chloride and sodium hypophosphite; and then the buffer or exaltant and the stablizing agent are added 1 thereto, as explained more fully hereinafter. The desired pH of the bath is established bytheeventual introduction thereinto of additional hydrochloric acid and is ap- For example, in the nickel plating of a steelobject, it is customary mechanically to clean the rust and mill scale from the object, to degrease the object, and then" lightly to pickle the object in a suitable acid, such aspropriately adjusted by the addition thereto of a weak alkali, preferably sodium bicarbonate.

The terms cation, anion, and ion as employed herein, except where specifically noted, include the total quantity of the corresponding elements that are present in the plating bath; i. e., both undissociated and dissociated material. In other words, 100% dissociation is assumed when the terms noted are used in connection with molar ratios and concentrations in the plating bath.

The stabilizing effects of the various organic compounds mentioned were determined from a series of plating tests that were made employing a standard test plating bath of the general character of that disclosed in the Gutzeit and Ramirez patent, except that the chemical ingredients were highly purified; this standard test plating bath had a volume of 50 cc. and a temperature between 98 C. and 100 C.; and therein low carbon steel samples were plated that had a surface area of 20 cm. and that had been vapor-degreased, electro-cleaned, and pickled in a HCl solution. The standard test plating bath was produced from a solution containing nickel as nickel hypophosphite (0.09 m. p. 1.), sodium hypophosphite (0.045 m. p. 1.), sodium succinate (0.06 m. p. 1.), sodium chloride (0.18 m. p. 1.), and enough water to make one liter, the pH having been adjusted to a value of 4.6 with pure HCl, whereby the nickel cation/hypophosphite anion ratio was 0.4. The stabilizing agents were then added to the standard test plating bath by measuring the proper volume from stock solutions containing 1,000 p. p. m. thereof; and the plating rates were measured in gm./cm. /min. In these tests stability is indicated by the time in minutes that elapsed before black precipitate was formed; and the appearance of the nickel deposited upon the samples was noted. In describing the appearance of a test sample, the following symbols are employed: B=semi-bright (satin); BB=bright; VB=very bright; S=smooth; SR=sligl1tly rough; R=rough; D= dull; and Sp=spotted.

Two blank plating tests were first run employing only the test samples in the standard test plating bath (without the addition of any stabilizing agent), with the following results:

Duration of test I 10 mm. I 60 min Weight gain, guns... 0. 0948 0. 1903 Plating rate RXIO'L .74 Sample appearance. B-S B-SR None 20 Time to black ppt., min

test plating bath containing sodium oleate as the stabiliz ing agent, the following results were obtained:

Stability test-60 minutes In a series of these plating tests employing the standard test plating bath containing potassium oleate as the stabilizing agent, the following results were obtained:

(a) Rate test-10 minutes p. p. m. of potassium oleate 0 25 Weight gain 0. 0596 0. 0577 0. 0542 .98 2.89 2. 71 BBS BB-S none none 4. 59 4. 59 4.02 07 (b) Stability test60 minutes p. p. m. potassium oleate. None 10 25 v 50 75 Wt. gain, gms 0.1253 0.1379 0. 1382 0.1392 0. 1483 pH begin 4. 58 4. 58 4. 58 4. 58 4. 58 pH end 2. 78 2. 2.66 2. 67 2. 62 Sample appear BB-S BB-S BB-S BB-S BB-S Time to black ppt., min. 10 10 15 15 50 In view of the foregoing plating tests employing the standard test plating bath containing either sodium oleate or potassium oleate, it is apparent that stabilization is achieved at 75 p. p. m.

A series of these plating tests were conducted employing the standard test plating bath containing a high molecular weight iminodazoline (Amine O, manufactured by Alrose Chemical Co.) as the stabilizing agent. Amine O is fundamentally 1 hydroxyethyl 2 heptadecenyliminodazoline of approximately 88% purity; and in these plating tests, the following results were obtained:

(a) Rate test-10 minutes p. p. In. of Amine O 0 1 5 I 10 Weight gain 0.0649. 0.0538. 0.0573. 0.0566. Plating rate 111x10 3.25..- 2.69... 2.87..... .83.

p. p. m. of Amine O 0 1 5 10 25 50 0.1341. 0.1361 0.1292 0.0995. BB-SR BB-S BBS SpS. l2 stab1e stable. 4.61 4.61 4.61 .61 4.61. 2.52-. 2.66. 2.88.. 3. 3.31.. 3.58. clear, green.. clear, greemclear, green.. clear, green. clear green clear, green.

the standard test plating bath containing as stabilizing In view of the foregoing plating tests employing in the agents the various organic compounds mentioned, the stabilizing agents being added to the baths from stock solutions containing 1,000 p. p. m. of the organic molecule.

In a series of these plating tests employing the standard standard test plating bath Amine O as the stabilizing agent, it will be observed that the stabilizing range is 5.0 p. p. m. and above, with acceptable rates up to 25 A series of these plating tests were conducted employing the standard test plating bath containing acetic acid salts of primary fatty amines (Armac T, manufactured by Armour & Co.) as the stabilizing agent. Armac T is fundamentally a tallow amineacetate consisting essentially of- 30% hexadecylamineacetate, 25% octadeeylamineacetate and 45% octadecenylamineacetate; and in these plating tests the following, results were obtained:

(a) Rate test10 minutes p. p. m. of Armac T 1 5 50 Weight gain 0.0649 010657 0.0008--. 0,0005. Plating rate R 10 3.25 3.29..- 0.04--- 0.03. Sample app Sp-S Sp-S Time to black ppt None None pH end pH begin.

Bath app Weight gain Sample app Time to black ppt 2171.. 2152-.. 3179 I 4141..- 454 clear, green. clear, green clear, green. clear, green Turbid,

green green In view of the foregoing plating tests employing in the standard test plating bath A'rmac T as the stabilizing agent, it will be observed that the stabilizing range is 5.0 p. p. m. and above, with an optimum rate at 5 p. p. m.

In a series of these plating tests employing the standard test plating bath containing a fatty amide sulfonate (Emcol X-25, manufactured by Emulsol Corp.) as the a stabilizing agent, the following results were obtained:

adverse action on the adhesion of the nickel plating upon the base metal of the plated bodies.

'In carrying out the present process in a continuous plating operation of the character of that disclosed in the Talmey and Crehan patent, it is recommended that the selected stabilizing agent be fed periodically or continuously into the plating bath along with the other regenerating chemicals (particularly the nickel cations and the hypophosphite anions) so as to keep the level thereof (a) Rate minutes 40 substantially constant and at that required, as previously explained. For example, the simplest and safest procedure is to select a stabilizing agent that is known to be active, 0 10 25 50 and not objectionable with respect to decreasing the plat- 4 4 6 444 44 ing rate over a relatively wide range of concentration, and i -$2 2 31 315566 I: 331?: 338? .1: 3:22": 3124. 45 then tokeep the level of concentration of the stabilizing Sample app BB-s.-. B agent within the effective range by the required addition g ?f i igi: thereof to the plating bath along with the other regenerat- H end-" 4 13"..- ing ingredients, as noted above. Bath c i green green green In view of the foregoing, it is apparent that there has been provided an improved process of chem1cal mckel (b) Stability testsminutes p.'p. m. of Emcol X-25. 0 1 5 10 25 50 Weight gain" 0.1506 0.1441 0.1432. 0.1462. 0.1453. Sample app... BB- B S BB-S -BBS. Time to black ppt. 20..-" 20. 55 Stable pH begin 4.61-

4.61-. 4.61 4.61-. 4.61. pH end. 2.41. 2.55 2.56 2.52--.-

2.54. Bath a p clear, green. clear, green. clear, green. clear, green. clear, green. clear, green.

-In view of the foregoing plating tests employing in the standard test plating bath Emcol X-25 as the stabilizing agent, it will be observed that the stabilizing range is 50.0 p. p. m. and above.

The minimum amounts of the different ones of these organic stabilizing agents that are required to achieve stabilization are a function of nickel cation concentration in the plating baths, whereby the minimum amount of the stabiliZingagent-that must be added thereto must be disproportionately increased as the nickel cation concentration in the plating bath isincreased. However, these minimum amounts of the different organic stabilizing agents are otherwise independent of the particuother constituents. This is probably due to the fact that plating of catalytic materials employing baths of the nickel cation-hypophosphite anion type containing stabilizing agents, as well as improved baths therefor. Further, it will be understood that great advantages are obtained by the utilization of the present process, particularly in continuous nickel plating operations, since such processes frequently involve exceedingly large volumes of the nickel plating bath that must be stabilized.

While there has been described what is at present considered to be the preferred embodiment of the invention, it will be understood that various modifications may be made therein, and it is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.

Thus

What is claimed is:

1. The process of chemically plating with nickel a solid body essentially comprising an element selected from the group consisting of iron, cobalt, nickel, aluminum, copper, silver, gold, palladium and platinum, which comprises contacting said body with a bath consisting essentially of an aqueous solution of a nickel salt and a I hypophosphite and an additive of the oriented hydrophobic film forming type, said additive comprising a long chain aliphatic organic compound in which the aliphatic radical contains from 8 to 18 carbon atoms, said additive being present in solution in said bath only in a controlled trace amount in the approximate range to 100 parts per 1,000,000 parts of said bath by weight so as not substantially to reduce the plating rate of said bath and so as to inhibit random decomposition of said bath.

2. The process of chemically plating with nickel a solid body essentially comprising an element selected from the group consisting of iron, cobalt, nickel, aluminum, copper, silver, gold, palladium and platinum, which comprises contacting said body with a bath comprising an aqueous solution of nickel ions and hypophosphite ions and an additive of the oriented hydrophobic film forming type, said additive comprising a long chain aliphatic organic compound in which the aliphatic radical contains from 8 to 18 carbon atoms, said additive being present in solution in said bath only in a controlled trace amount in the approximate range 5 to 100 parts per 1,000,000 parts of said bath by weight so as not substantially to reduce the plating rate of said bath and so as to inhibit random decomposition of said bath.

3. The process set forth in claim 2, wherein said organic compound is selected from the class consisting of fatty acids and water-soluble salts thereof, amino compounds, and sulfates and sulfonates of fatty acids and fatty alcohols.

4. The process set forth in claim 2, wherein said organic compound is selected from the class consisting of fatty acids and water-soluble salts thereof.

5. The process set forth in claim 2, wherein said organic compound is selected from the class consisting of amino compounds.

6. The process set forth in claim 2, wherein said organic compound is selected from the class consisting of sulfates and sulfonates of fatty acids and fatty alcohols.

7. A bath for the chemical plating of a catalytic material with nickel comprising an aqueous solution of nickel ions and hypophosphite ions and an additive of the oriented hyprophobic film forming type, said additive comprising a long chain aliphatic organic compound in which the aliphatic radical contains from 8 to 18 carbon atoms, said additive being present in solution in said bath only in a controlled trace amount in the approximate range 5 to parts per 1,000,000 parts of said bath by Weight so as not substantially to reduce the plating rate of said bath and so as to inhibit random decomposition of said bath.

8. The bath set forth in claim 7, wherein said organic compound is selected from the class consisting of fatty acids and water-soluble salts thereof, amino compounds, and sulfates and sulfonates of fatty acids and fatty a1- cohols.

9. The bath set forth in claim 7, wherein said organic compound is selected from the class consisting of fatty acids and water-soluble salts thereof.

10. The bath set forth in claim 7, wherein said organic compound is selected from the class consisting of amino compounds.

11. The bath set forth in claim 7, wherein said organic compound is selected from the class consisting of sulfates and sulfonates of fatty acids and fatty alcohols.

References Cited in the file of this patent UNITED STATES PATENTS 2,532,283 Brenner Dec. 5, 1950 

1. THE PROCESS OF CHEMICALLY PLATING WITH NICKEL A SOLID BODY ESSENTIALLY COMPRISING AN ELEMENT SELECTED FROM THE GROUP CONSISTING OF IRON, COBALT, NICKEL, ALUMINUM, COPPER, SILVER, GOLD, PALLADIUM AND PLATINUM, WHICH COMPRISES CONTACTING SSAID BODY WITH A BATHS CONSISTING ESSENTIALLY OF AN AQUEOUS SOLUTION OF A NICKEL SALT AND A HYPOPHOSPHITE AND AN ADDITIVE OF THE ORIENTED HYDROPHOBIC FILM FORMING TYPE, SAID ADDITIVE COMPRISING SA LONG CHAIN ALIPHATIC ORGANIC COMPOUND IN WHICH THE ALIPHATIC RADICAL CONTAINS FROSM 8 TO 18 CARBON ATOMS, SAID ADDITIVE BEING PRESENT IN SOLUTION IN SAID BATH ONLY IN A CONTROLLED TRACE AMOUNT IN THE APPROXIMATE RANGE 5 TO 100 PARTS PER 1,000,000 PARTS OF SAID BATH BY WEIGHT SO AS NOT SUBSTANTIALLY TO REDUCE THE PLATING RASTE OF SAID BATH AND SO AS TO INHIBIT RANDOM DECOMPOSITION OF SAID BATH. 